Showing papers on "Orthorhombic crystal system published in 1988"
TL;DR: In this article, the crystal structure of LiSbWO6 was solved from X-ray powder diffraction data and the structure was refined using Rietveld profile refinement principles.
2,325 citations
TL;DR: A new superconductor that displays onset behavior near 120 K has been identified as Bi2Sr3-xCaxCu2O8+y, with x ranging from about 0.4 to 0.9, and electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension.
Abstract: A new superconductor that displays onset behavior near 120 K has been identified as Bi2Sr3-xCaxCu2O8+y, with x ranging from about 0.4 to 0.9. Single crystal x-ray diffraction data were used to determine a pseudo-tetragonal structure based on an A-centered orthorhombic subcell with a = 5.399 A, b= 5.414A, and c = 30.904 A. The structure contains copper-oxygen sheets as in La2CuO4 and YBa2Cu3O7, but the copper-oxygen chains present in YBa2Cu3O7 do not occur in Bi2Sr3-xCaxCu2O8+y. The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca2+ and Sr2+ cations between the adjacent Cu-O sheets; Sr2+ cations are also found between the Cu-O and Bi-O sheets. Electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension. This superstructure is also observed by x-ray diffraction on single crystals, but twinning can make it appear that the superstructure is along both a and b axes. Flux exclusion begins in our samples at about 116 K and is very strong by 95 K. Electrical measurements on a single crystal of Bi2Sr3-xCaxCu2O8+y show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.
623 citations
TL;DR: Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high-Tc phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate as mentioned in this paper.
Abstract: Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high-Tc phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate. The sharp powder X-ray diffraction pattern obtained from well-grown particles, 5~10 µm wide and 0.5 µm thick typically, was assigned to an orthorhombic cell with a=0.537 nm, b=2.682 nm, and c=3.726 nm. The electrical resistance dropped to zero at 107 K within the experimental limit of 10-6 Ω. A large diamagnetic response in the ac susceptibility due to the Meissner effect was seen below 120 K. The dominance of the high-Tc phase over the low-Tc phase was roughly estimated at 9/1 in volume.
579 citations
TL;DR: X-ray diffraction and electron microscopy data are consistent with a structure of alternating perovskite and Bi-Ca-Sr-Cu-O layers, which reveals a b-axis superstructure of 27.2 A, numerous stacking faults, and other defects.
Abstract: Four phases are observed in superconducting Bi-Ca-Sr-Cu-O samples. The superconducting phase, with onset temperature near 120 K, is a 15.4-A-layered compound with composition near Bi2Ca1Sr2Cu2O9 and an A-centered orthorhombic unit subcell 5.41 x 5.44 x 30.78 A. X-ray diffraction and electron microscopy data are consistent with a structure of alternating perovskite and Bi2O2 layers. High-resolution transmission electron microscopy images reveal a b-axis superstructure of 27.2 A, numerous (001) stacking faults, and other defects.
500 citations
TL;DR: An ordered orthorhombic phase has been detected in a Ti-25at.% Al-12.5at. alloy as discussed by the authors, which is one of a family of Ti3Al base alloys under development for high temperature applications.
497 citations
TL;DR: The structure of the title compound, Sr8Ca6Cu24O41 and Sr14Cu 24O41, has been determined by x-ray, single-crystal diffraction techniques as discussed by the authors.
305 citations
TL;DR: In this paper, the structure of orthorhombic YBa2Cu3O7 was refined in the temperature interval 5-320K, to an accuracy higher by a factor of about two compared to previous refinements.
181 citations
TL;DR: In this paper, a model for the modulated crystal structure in high-Tc superconductor in a Bi-Sr-Ca-Cu-O system is proposed based on the high-resolution electron microscope images.
Abstract: A model for the modulated crystal structure (Matsui et al.: Jpn. J. Appl. Phys. in press) in high-Tc superconductor in a Bi-Sr-Ca-Cu-O system is proposed based on the high-resolution electron microscope images. Ideally, it is body-centered orthorhombic with a=0.54, b=5a=2.7 and c=3.08 nm. The Bi2O2 layers do not form complete sheets, but contain occupational and/or positional fluctuation of Bi-sites to form "Bi-concentrated bands" which extend in the a-direction. Contraction of lattice planes along the b-axis is induced in the Bi-concentrated bands, causing compensating expansion in the remaining Bi-deficient ones.
157 citations
TL;DR: In this paper, the compound of formula YBa 2 Cu 2.7 Fe 0.3 O 7.13 has been analyzed by neutron and electron diffraction techniques, and the results indicate that Fe 3+ is present in tetrahedral coordination and Fe 4+ in pyramidal and octahedral coordination.
152 citations
TL;DR: In this article, the experimental background for a high temperature neutron powder diffraction study of transition metal hemicarbides M2C1−x having various compositions was presented, and the results showed that the disordering of this ϵ-phase occurs through a second order transition at elevated temperatures.
120 citations
TL;DR: In this article, the locations of the dopant atoms, Ni, Zn and Co, in the 1-2-3 (Y/Ba/Cu) oxide were determined by means of X-ray and time-of-flight type (TOF) neutron diffractometers.
Abstract: A structural study of orthorhombic YBa2Cu3O6.94, YBa2Cu2.8Ni0.2O6.85 and YBa2Cu2.7Zn0.3O6.75, and tetragonal YBa2Cu2CoO7.16 by means of X-ray and time-of-flight type (TOF) neutron diffractometers was carried out to determine the locations of the dopant atoms, Ni, Zn and Co, in the 1-2-3 (Y/Ba/Cu) oxide. The nickel atoms occupy only the Cu2 site 2q(00z) with z=0.36. The zinc atoms occupy the Cu1 site 1a(000) and the Cu2 site with occupancies of 0.20(5) and 0.05(2). In the tetragonal YBa2Cu2CoO7.16, cobalt atoms were found at both the Cu1 and Cu2 sites with occupancies of 0.83(2) and 0.08(1).
TL;DR: In this paper, the crystal and defect-structure of YBa2(Cu0.97Fe0.03)2(cu0.86Fe 0.1□0.04)O7 was studied using single crystal and powder X-ray diffraction, powder neutron diffraction at room temperature and 3 K.
Abstract: Single crystal- and powder X-ray diffraction, powder neutron diffraction at room temperature and 3 K, high resolution electron microscopy and electron diffraction were used to study the crystal- and defect-structure of YBa2(Cu0.93Fe0.05)3O7. Crystals of this compound are superconducting (T
c
≈80 K) and appeart to be tetragonal down to at least 3 K. The structure resembles that of the undoped YBa2Cu3O7 phase with the oxygen content being very close to 7.0 and the Fe atoms preferentially occupying the Cu(1) site. A copper deficiency is shown to be present on this site too, leading to the approximate formula YBa2(Cu0.97Fe0.03)2(Cu0.86Fe0.1□0.04)O7. High resolution electron microscopy reveals the existence of orthorhombic micro-domains, 20–30 A in diameter, probably due to short range ordering of oxygen atoms on the O(1) site. In view of these results the structure has to be regarded as being tetragonal only in a statistical sense.
TL;DR: A detailed study of the superconducting properties and crystal symmetry of YBa2Cu3Ox as a function of oxygen content (x) is presented in this paper, where it is shown that the orthorhombic to tetragonal phase transition coincides with a loss in superconductivity for samples prepared both by quenching from high temperature and samples prepared by deoxygenation at low temperature.
TL;DR: In this paper, the concentration changes which accompanied the crystal growth of hen egg-white lysozyme from its aqueous solution were followed optically at 5, 10, 15, 30, 42, and 50°C for 30-360 days in the presence of 1-7% NaCl.
TL;DR: In this paper, the Nd1+xBa2-xCu3O7-δ system has been investigated by X-ray powder diffraction combined with Rietveld analysis.
Abstract: Crystal structures in the Nd1+xBa2-xCu3O7-δ system have been investigated by X-ray powder diffraction combined with Rietveld analysis The compound NdBa2Cu3O7-δ is isomorphic with orthorhombic YBa2Cu3O7-δ With the increase of x the orthorhombic distortion decreases, and the compound becomes tetragonal at x=02 The tetragonal structure is isomorphic with the tetragonal form of YBa2Cu3O7-δ Tc of the compounds with x=0 and 005 is above 90 K, which decreases monotonically with x and the compound becomes semiconducting at x=04
TL;DR: In this paper, the metastable phase β-AlF3 was solved by X-ray powder and single-crystal diffraction methods, and the crystal habit is pseudo-hexagonal with systematic twinning (rotation of 120° around the c axis), but the true symmetry is orthorhombic with space group Cmcm, Z = 12, a = 6.931(3), b = 12.492(4), c = 7.534(5), A = 0.
TL;DR: In this article, the impurity-induced orthorhombic to tetragonal transition observed by X-ray diffraction measurements can be explained as resulting from the specific structure: each domain possesses the orthorHombic structure including 1-D Cu-O chains ordered along the [100] or [010] direction, and two orientation variants are mixed coherently leading to an "averaged" tetragon symmetry as observed by diffraction methods.
Abstract: The Fe-doped high-Tc superconducting phase YBa2(Cu1-xFex)3O7-y has been investigated by electron microscopy. The sample with x=0.04 shows a microdomain structure composed of ordered domains with sizes of about 5 nm, while an ordinary striped twin pattern is observed for x=0.02. The impurity-induced orthorhombic to tetragonal transition observed by X-ray diffraction measurements can be explained as resulting from the specific structure: Each domain possesses the orthorhombic structure including 1-D Cu-O chains ordered along the [100] or [010] direction, and two orientation variants are mixed coherently leading to an "averaged" tetragonal symmetry as observed by diffraction methods.
TL;DR: In this article, a series of 10 glasses on or near the Y2O3-SiO2-AIN plane of the Y-Si-Al-O-N system was found to be strongly dependent on composition with the best glassforming characteristics occurring in a glass having a normalized composition of Y0.26Si0.30Al0.11ON0.
Abstract: Glass formation for a series of 10 glasses on or near the Y2O3-SiO2-AIN plane of the Y-Si-Al-O-N system was found to be strongly dependent on composition with the best glassforming characteristics occurring in a glass having a normalized composition of Y0.26Si0.30Al0.11ON0.11. Crystallization of this glass was found to proceed by a heterogeneous nucleation mechanism, with intermetallic iron silicides acting as nuclei for the columnar dendritic y-Y2Si2O7 species. Secondary crystallization of a species having a nominal composition of YSi2AIO4N2 occurred in interdendritic regions when crystallization temperatures approached 1200°C. A third stage of crystallization involved the formation of the high-temperature polymorph of Y2Si2O7 (δ2-Y2Si2O7) through transformation of the y-Y2Si2O7 dendrites to an intermediate product (δ2-Y2Si2O7) followed by recrystallization to the δ1-Y2Si2O7 polymorph. Convergent-beam electron diffraction results for the crystal structure determination of y-Y2Si2O7 showed it to be based on an end-centered orthorhombic Bravais lattice having unit-cell dimensions of a= 0.806 nm, b= 0.934 nm, and c= 0.692 nm with a space group of Aba2. A similar determination for δ2-Y2Si2O7 showed it to be based on a primitive orthorhombic Bravais lattice having unit-cell dimensions of a=1.36 nm, b= 0.501 nm, and c= 0.815 nm with a space group of Pna21.
TL;DR: In this paper, the magnetic ordering in the high-temperature superconducting compound GdBa/sub 2/Cu/sub 3/O/sub 7 was investigated and it was shown that the ordered magnetic moment per Gd atom lies along the c axis of the orthorhombic cell.
Abstract: Neutron diffraction has been employed to study the magnetic ordering in the high-temperature superconducting compound GdBa/sub 2/Cu/sub 3/O/sub 7/. The compound is found to undergo an antiferromagnetic transition with the Gd magnetic moments ordering at 2.22 +- 0.07 K. The ordering is shown to be three dimensional with a doubling of the orthorhombic unit in all three directions. An analysis of the intensities of the observed magnetic Bragg reflections shows that the ordered magnetic moment per Gd atom is 7.4 +- 0.6..mu../sub B/ and lies along the c axis of the orthorhombic cell. It is unlikely that dipolar ordering can explain the occurrence of this magnetic phase transition where the system locks into a three-dimensional ordered arrangement at the Neel temperature, since the separation of the Gd atoms along the c axis is approximately three times that along the a,b axes.
TL;DR: In this paper, the authors obtained Raman spectra for a number of orthorhombic perovskites CaBO3, where B=Ti, Ge, Zr or Sn.
Abstract: We have obtained Raman spectra for a number of orthorhombic perovskites CaBO3, where B=Ti, Ge, Zr or Sn. The room temperature Raman spectrum of CaTiO3 was compared with cubic SrTiO3 to assign first- and second-order features. Partially polarized micro-Raman spectra were obtained for CaTiO3 perovskite. The CaBO3 perovskites showed a sequence of increasing complexity in their Raman spectra with increasing degree of orthorhombic distortion from the ideal cubic structure. The spectral changes cannot easily be correlated with changes in chemistry or structure of the perovskite. High temperature micro-Raman spectra for CaGeO3 perovskite were obtained by laser-heating a 15 μm sample. None of the low frequency Raman modes were soft, but showed only normal anharmonicity up to approximately 700 K.
TL;DR: In this article, different samples of Tl 2 Ba 2 Cu 1 O 6 have been prepared by different heat treatments at relatively low temperature, and the main difference between the various samples appears to be that the non-superconducting material is orthorhombic, with a well ordered superstructure, while the superconducting materials is pseudo-tetragonal, with disordered oxygen within the TlO plane.
Abstract: Many different samples of Tl 2 Ba 2 Cu 1 O 6 have been prepared by different heat treatments at relatively low temperature. The material as first prepared is clearly orthorhombic and non-superconducting, but on annealing and quenching, the samples become almost tetragonal with high T c . Various T c values between 3+ O 2- atoms are missing, creating the electron holes apparently necessary for superconductivity. The main difference between the various samples appears to be that the non-superconducting material is orthorhombic, with a well ordered superstructure, while the superconducting material is pseudo-tetragonal, with disordered oxygen within the TlO plane, as for the higher superconducting members of the Tl 2 Ca n Ba 2 Cu n +1 O 2( n +3 ) series. Superconductivity then appears to depend on the precise structural arrangement, and not just on stoichiometry and the number of electron holes.
TL;DR: Mossbauer spectroscopy of 57 Fe in both tetragonal and othorhombic phases of YBa 2 (Fe x Cu 1− x ) 3 O 7− δ, with x = 0.01, 0.02 and 0.10, at temperatures 4.2 K, 75 K, 90 K, and 300 K have been performed as mentioned in this paper.
TL;DR: In this article, the crystal and molecular structure of BeH 2 was determined from high-resolution powder diffraction data obtained at a synchrotron radiation source, based on a network of corner-sharing BeH 4 tetrahedra.
TL;DR: In this article, two types of aluminosilicate gels have been synthesized by using different precursors and by varying pH and water content during the gelification process.
Abstract: Earlier works of mullitization through the gel route have been reviewed and the results show 980°C DTA and crystalline phases. Some Al2O3-SiO2 gels have been synthesized by using different precursors and by varying pH and water content during the gelification process. Thermal changes of these coherent gels were studied by DTA and X-ray powder diffractometry. The results demonstrate that two types of aluminosilicate gels form. The first type produces orthorhombic mullite directly on heating at 980°C, whereas the second type forms cubic mullite first at 980°C and then transforms to the orthorhombic variety on further heating. Lastly, the cause of the 980°C exotherm is explained with reference to kaolinite.
TL;DR: In this paper, the superconducting transition temperature Tc and normal-state resistivity have been investigated as a function of x for the Nd1+xBa2-xCu3O7-? system, whose crystal structures have been determined at room temperature by X-ray powder diffraction combined with the Rietveld method.
Abstract: The superconducting transition temperature Tc and normal-state resistivity have been investigated as a function of x for the Nd1+xBa2-xCu3O7-? system, whose crystal structures have been determined at room temperature by X-ray powder diffraction combined with the Rietveld method. Tc of the samples with x=0 and 0.05 is above 90 K, which decreases monotonically with x except for around x=0.25?0.30 (Tc?35 K) and the sample becomes semiconducting at x=0.40. The orthorhombic distortion of the compounds decreases with x and the compound becomes tetragonal at x=0.20. The variation of Tc with x is insensitive to the orthorhombic-tetragonal phase transition. A correlation of Tc with hole concentration in copper-oxide-type superconductors is discussed based on a possible hole concentration compensation effect of excess Nd.
TL;DR: The structure of Bi 2 O 2 CO 3 has been investigated using powder neutron diffraction as discussed by the authors, and not all observed peaks could be indexed on the previously reported tetragonal unit cell, and a larger orthorhombic cell was adopted (Pna2 1, a=5.468(1), b=27.32(2), c =5.68(1) A ).
TL;DR: In this paper, the crystal structure of the high-Tc Bi2-x(Ca, Sr)3Cu2+xO9-y with x = 0.2 and y=0.78 was studied by means of neutron and X-ray powder diffraction.
Abstract: The crystal structure of the high-Tc Bi2-x(Ca, Sr)3Cu2+xO9-y with x=0.2 and y=0.78 was studied by means of neutron and X-ray powder diffraction. Since the unit cell parameters were relatively large for powder diffraction analysis, an averaged structure was refined, assuming an orthorhombic sub-cell (a=5.39 A, b=5.39 A and c=30.37 A) which corresponds to 1/5 of the unit cell: This is a derivative of Bi4Ti3O12. The double perovskite unit interleaved by the double bismuth layers is B-type, i.e. a CuO6 octahedron is surrounded by eight alkaline earth metal ions. The pyramidal CuO5 configuration is found in this oxide. The copper valency is estimated at about 2.3 on the basis of the determined chemical composition.
TL;DR: In this article, a twin structure with twin plane (510) and with the composition plane (001) is observed in a high-Tc Bi-Sr-Ca-Cu-O superconductor which is orthorhombic with a=0.54, b=2.7 and c=3.08 nm.
Abstract: Twinned structure with twin plane (510) and with the composition plane (001) is observed in a high-Tc Bi-Sr-Ca-Cu-O superconductor which is orthorhombic with a=0.54, b=2.7 and c=3.08 nm. Directions of "Bi-concentrated bands" in both twin individuals are perpendicular to each other. Local intergrowths of perovskite-related layers with 1.8 and 2.1 nm thickness are observed among the major layers of 1.5 nm. The material includes small amounts of crystal with c=3.6 nm, which may be responsible for the superconductivity at 105 K, as already suggested by Muromachi et al. (Jpn. J. Appl. Phys. 27 (1988) L556).
TL;DR: In this paper, the phonon spectrum in YBa/sub 2/Cu/sub 3/O/sub 7/ was calculated in the orthorhombic structure using an unscreened rigid-ion model as a first approximation.
Abstract: The phonon spectrum in YBa/sub 2/Cu/sub 3/O/sub 7/ is calculated in the orthorhombic structure using an unscreened rigid-ion model as a first approximation. The calculated values of the ''neutron-weighted'' phonon density of states, the optical frequencies, the Debye temperature, and the mean-squared vibrational amplitudes are in fair agreement with the values reported from various experiments.
TL;DR: In this article, a misfit layer structure consisting of two-atom thick layers of SnS with distorted NaCl type structure and three-atom-thick sandwiches of NbS2 was described.